Update for those interested in resolving. I tried using vista's built in utility Reg.exe.

Syntax: Reg load hklm\test c:\test\ntuser.dat.
Works.

next

Reg load hklm\test \\server\share\folder\ntuser.dat
access denied
doesn't work

Loading a dat file from a UNC path seems to not work. Is this by design under vista?

Earlier I think I stated that loading the hive locally didn't work. I got confused in my testing. I really would like to make this run from a UNC path rather than copy the file locally, modify it, and then overwrite the existing file at the UNC location.

Once again sorry about the earlier confusion and thanks for any help.